STEFFEN, T. ... et al, 2009. High redundancy in actuation. Presented at SET for Britain, House of Commons, 9th March 2009

Abstract:

Actuation, the controlled movement and positioning of objects, is an essential function of many technical systems. It is crucial in many applications from central heating to aircrafts, and without actuation, the function or even the safety of the system would suffers. For example an aircraft is steered using control surfaces, and if the actuation of these surfaces fails, the aircraft may crash.
Therefore, actuation is often provided by using several (typically between 2 and 4) redundant actuation elements. If one element fails, another takes over, and harm can be avoided. While this solution works, it involves increased cost, weight and energy use, reducing the efficiency of the system considerable.
This project on high redundancy actuation investigates the use of a high number of actuation elements, such as 10 or even 100. This is a bionic (or bio-mimetic) idea: the use of actuation elements is similar to the composition of a muscle from many individual muscle fibres. Just like the muscle is highly resilient to damage in individual fibres (causing sore muscles, but no loss of movement), high redundancy actuation is highly reliable even if several elements have failed.
The reliability analysis shows that this approach provides the same level or even superior protection against faults, without the loss of efficiency involved in the traditional solution. The basic advantage is that the law of large numbers applies, which provides a much more accurate prediction of how faults will affect the actuation elements over time. In the aircraft example, this would provide lighter actuators that provide superior reliability, leading to better fuel economy and easier maintenance.
The main scientific problem of this project is how to deal with the complexity of using a high number of elements together. The results show that it is possible to determine the reliability of the system, and it is also possible to control the many elements as if they are just one big actuator. The next phase of the project is dealing with the technological challenges of combining many actuation elements. A simple experiment with four elements has been completed, and a demonstrator with 16 elements is being built. These experiments are used to demonstrate the resilience to faults, and understand the practical control issues at hand.
A project leading to a more advanced version with up to 100 elements is currently being prepared. While the developed theories can be extended easily to consider such configurations, the practical difficulties of designing and manufacturing such a solution are challenging. The goal is to demonstrate that high redundancy actuation is feasible with the currently available technology, and to get an idea of the manufacturing issues involved.

Description:

The poster was presented at at SET for Britain in the Parliament 9th March 2009 (http://www.setforbritain.org.uk/) by
Thomas Steffen, representing the six members of staff from the Control Systems Group. This poster is also available at: http://www-staff.lboro.ac.uk/~elts2/tmp/set-poster250.png

Sponsor:

This project is funded by the UK Engineering and Physical Sciences Research
Council (EPSRC) under grant EP/D078350/1 (2007-2009). It is performed
together with our two industrial partners BAE Systems and SMAC UK ltd.
Systems Engineering Innovation Centre.